Gearbox for gas turbine engine

1. A method of operating a gas turbine engine having a shaft rotatable about a central axis, a compressor, and a gearbox, the method comprising:

rotating one of a sun gear, a planet carrier rotatably supporting planet gears meshed with the sun gear, and a ring gear meshed with the planet gears of the gearbox with the shaft and driving the compressor with another one of the sun gear, the planet carrier, and the ring gear of the gearbox; and

operating the gearbox in a selected one of a speed change configuration in which a rotational speed ratio between the compressor and the shaft is different than 1 and a direct drive configuration in which the rotational speed ratio between the compressor and the shaft is 1, the compressor drivingly engaged to the shaft via the gearbox in both of the speed change configuration and the direct drive configuration, wherein the operating of the gearbox in the direct drive configuration includes allowing rotation of an intermediate rotatable component corresponding to yet another one of the sun gear, the planet carrier, and the ring gear, and limiting rotation of the planet gears about rotation axes thereof, and wherein the operating of the gearbox in the speed change configuration includes limiting rotation of the intermediate rotatable component, and allowing rotation of the planet gears about their respective rotation axes.

2. The method of claim 1 , wherein the operating of the gearbox in the speed change configuration includes increasing a rotational speed of the compressor relative to that of the shaft.

3. The method of claim 1 , wherein the operating of the gearbox in the speed change configuration includes decreasing a rotational speed of the compressor relative to that of the shaft.

4. The method of claim 1 , wherein the limiting of the rotation of the planet gears about the rotation axes includes applying a braking force directly on the planet gears.

5. The method of claim 1 , wherein the limiting of the rotation of the planet gears about the rotation axes includes limiting rotation of the rotatable intermediate component relative to the other one of the sun gear, the planet carrier, and the ring gear.

6. The method of claim 5 , wherein the limiting of the rotation of the planet gears about the rotation axes includes drivingly engaging the rotatable intermediate component to the other one of the sun gear, the planet carrier, and the ring gear.

7. A method of operating a gas turbine engine having a shaft rotatable about a central axis, a compressor, and a gearbox, the method comprising:

rotating a first gear of the gearbox with the shaft, the first gear meshed with first planet gears, the first planet gears engaged to second planet gears and rotatably supported by a planet carrier;

driving the compressor with one of the planet carrier and a second gear meshed with the second planet gears; and

operating the gearbox in a selected one of a speed change configuration in which a rotational speed ratio between the compressor and the shaft is different than 1 and a direct drive configuration in which the rotational speed ratio between the compressor and the shaft is 1, the compressor drivingly engaged to the shaft via the gearbox in both of the speed change configuration and the direct drive configuration, wherein the operating of the gearbox in the direct drive configuration includes allowing rotation of the other of the planet carrier and the second gear and limiting rotation of the first and second planet gears about respective rotation axes, and wherein the operating of the gearbox in the speed change configuration includes limiting rotation of the other of the planet carrier and the second gear and allowing rotation of the first and second planet gears about the respective rotation axes.

8. The method of claim 7 , wherein the limiting of the rotation of the first and second planet gears includes limiting rotation of the planet carrier relative to the second gear.

9. The method of claim 7 , wherein the first gear is a first sun gear and the second gear is a second sun gear, transmitting the rotational input from the shaft to the first gear includes transmitting the rotational input to the first sun gear, and transmitting the rotational output to the compressor includes transmitting the rotational output to the compressor from the one of the planet carrier and the second sun gear.

10. The method of claim 7 , wherein the first gear is a first ring gear and the second gear is a second ring gear, transmitting the rotational input from the shaft to the first gear includes transmitting the rotational input to the first ring gear, and transmitting the rotational output to the compressor includes transmitting the rotational output to the compressor from the one of the planet carrier and the second ring gear.

11. A method of operating a gas turbine engine having a shaft rotatable about a central axis, a compressor, and a gearbox engaging the shaft to the compressor, the method comprising:

rotating one of a sun gear, a planet carrier rotatably supporting planet gears meshed with the sun gear, and a ring gear meshed with the planet gears of the gearbox with the shaft and driving the compressor with another one of the sun gear, the planet carrier, and the ring gear of the gearbox, the driving of the compressor includes rotating the compressor at a first rotational speed corresponding to that of the shaft by allowing rotation of an intermediate rotatable component corresponding to yet another one of the sun gear, the planet carrier, and the ring gear, and limiting rotation of the planet gears about rotation axes thereof;

determining that the gas turbine engine is in need of a boost; and

changing a rotational speed of the compressor from the first rotational speed to a second rotational speed greater than the first rotational speed, wherein the changing of the rotational speed includes limiting rotation of the intermediate rotatable component, and allowing rotation of the planet gears about their respective rotation axes.

12. The method of claim 11 , wherein the determining that the gas turbine engine is in need of the boost includes one or more of determining that another gas turbine engine is inoperative, determining that the gas turbine engine is operating in a hot temperature condition, and determining that the gas turbine engine is operating in a high altitude.

13. The method of claim 11 , wherein the limiting of the rotation of the planet gears about the rotation axes includes applying a braking force directly on the planet gears.

14. The method of claim 11 , wherein the limiting of the rotation of the planet gears about the rotation axes includes limiting rotation of the rotatable intermediate component relative to the other one of the sun gear, the planet carrier, and the ring gear.

15. The method of claim 14 , wherein the limiting of the rotation of the planet gears about the rotation axes includes drivingly engaging the rotatable intermediate component to the other one of the sun gear, the planet carrier, and the ring gear.